Players' association heads for the NFL, NBA, NHL and Major League Baseball asked "good questions" during private meetings with gaming officials that were centered on the possibility of expanded legalized sports betting in the United States, and what that would mean for their respective leagues and athletes.

The American Gaming Association on Monday said it had taken part in meetings with the players' associations, discussing how legal sports betting works in international jurisdictions, data rights and potential marketing opportunities for players with legal betting entities.

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The players' unions of the NFL, NBA, MLB and NHL have been meeting over the past year-and-a-half to discuss the impact that legalized sports gambling could have on players, according to a report by The MMQB.

"I think what the unions are trying to do now, wisely, is learn everything they can learn [about regulated sports betting]," Geoff Freeman, president and CEO of the American Gaming Association, said on a Monday press call to announce the formation of the American Sports Betting Coalition.

Freeman said the unions are taking the issue of legalized sports betting "seriously" and are aware of studies that show sports betting increases fan engagement and viewership.

"I can tell you from the questions they asked us, they were good questions," Freeman said. "They're thoughtful on this. They're going to be a key stakeholder on how this plays out."

MMQB.com reported meetings between the union heads on sports betting took place over the last 18 months in New York. The NFLPA's DeMaurice Smith, the MLBPA's Tony Clark, the NBPA's Michele Roberts and the NHLPA's Donald Fehr were reportedly in attendance.

"Yes, the sports unions have been discussing the issue, in particular around the integrity of our respective games," NFLPA executive George Atallah told MMQB.com. "We're collaborating on it. We might be open to changes that are coming because of [legalized sports gambling], but before we get to the revenue aspect of it, do we have the infrastructure in place to prevent any sort of shenanigans? That's the issue."

Sports betting is currently legal in just a handful of states, with only Nevada being able to offer a full menu of wagers. The American Sports Betting Coalition -- which consists of law enforcement, states' rights advocates and gaming industry leaders -- is aiming to lobby Congress to lift the federal prohibition on regulated sports betting.

Missing from the coalition, though, are any of the sports leagues. The NBA, led by commissioner Adam Silver, has pivoted its position on sports betting and now believes a regulated market would better protect the integrity of the games. Major League Baseball, Major League Soccer and the PGA Tour also have expressed a willingness to re-examine how sports betting is approached in the U.S.

The NHL has remained mostly quiet on the issue, even with the expansion Vegas Golden Knights preparing for their inaugural season. The NFL and NCAA remain opposed to expanding legal sports betting in the U.S.

"The best way, I think, for the leagues to demonstrate their commitment to this is not necessarily as a part of this coalition," Freeman said. "It's working with the gaming industry, working with other stakeholders to come to an agreement on all the sticky issues that come with this."